2013 Silverado gear swap

[mason_smith818]

Hey guys. I just bought a 2013 Silverado z71 leveled on 35’s. I noticed it was really sluggish in comparison to my other buddies 07-13 trucks. Well, come to find out, the truck has 3.08 gears. I’m really wanting to make the jump to at least a 3.73, and had a couple questions as this is my first GM truck I have ever owned. 
1. Instead of changing the actual ring and pinion, could I buy an entire used 3.73 axle for the rear, and just re-gear the front chunk, in turn saving money? 
 

2. Will any 07-13 1500 rear axle actually work and fit if I did go this route? (I guess what I’m trying to ask is if they’re interchangeable or if something differs between any of them, or was changed over the years these trucks were produced). 
 

3. Is a tune mandatory afterwards for the truck to run out and shift correctly? (I’m not used to trucks with so many electronically controlled parts, lol). I’m not really concerned with the speedometer being if that would be the only issue. 
 

Thanks in advance guys. 

[davester]

Yeah, finding the same diff with a different ratio would be the way to go.  You might want to also make sure it has the locker you want (open diff, G80, or some other locker [harder to find]).  If you want a specific locker other than the G80, then you probably want to go with just doing the gears and locker in your current housing.

 

You could also look around for a front diff with 3.73 as well, and just swap it in.

 

I don't know anything about which diffs would be bolt in swap for your truck.

Edited December 10, 2020 by davester

[mason_smith818]

41 minutes ago, davester said:

Yeah, finding the same diff with a different ratio would be the way to go.  You might want to also make sure it has the locker you want (open diff, G80, or some other locker [harder to find]).  If you want a specific locker other than the G80, then you probably want to go with just doing the gears and locker in your current housing.

 

You could also look around for a front diff with 3.73 as well, and just swap it in.

 

I don't know anything about which diffs would be bolt in swap for your truck.

I figured it would be a lot easier to do it that way. Heck, they might all be the same no matter the gear ratio. As long as the housings are the same, I don’t imagine having any problems as far as fitment would go. But want to be sure before I pull the trigger. 

[CamGTP]

Yes, it needs to be in the correct year range because of the ABS system on the rear axles.

 

Yes,  you must tune the computer for this. That is a huge jump in gear size and it will throw the transmission way of whack with shift timing and shift speeds.

Edited December 10, 2020 by CamGTP

[mason_smith818]

27 minutes ago, CamGTP said:

Yes, it needs to be in the correct year range because of the ABS system on the rear axles.

 

Yes,  you must tune the computer for this. That is a huge jump in gear size and it will throw the transmission way of whack with shift timing and shift speeds.

Okay. 
 

As far as the tuning goes, would it necessarily have to be a “custom tune” from a tuner. Or would a standard mechanic shop be able to make it work with a standard flash? Also, if it does have to be a custom tune, could I limp it home from the shop until I could get a tune for it? 

[CamGTP]

Would have to be a custom tune or a done with a handheld tuner from like Diablo, HyperTech or similar.

 

A mechanics shop or dealership can't change the gear ratio in the calibration. If they are only allowed to use a GM tool like a Tech 2 or GM MDI they can only program the computer with the factory operating system file that is tied to your VIN on the truck.

 

It could still be limped home, it's just not going to act correctly because of the changes.

[Jsdirt]

Keep in mind, some GMT-900 truck rear ends still use drum brakes - mine is one of them. Parking brake and brake line hookups are TOTALLY different. Not sure what the RPO code is ( IF there even is one ) for a drum brake axle. The RPO will tell you gearing, too. If you get a used one with the G80, either remove or rebuild that locker unit. They're utter garbage. 

 

When my  spider gears shed the tips of their teeth off at 97k miles (that's when I discovered it - could've happed 10 years ago ...), nearly every clutch in the G80 pack was down to bare metal.

 

 Swapping out the assembly is the way to go for technical ease. Just make sure you get a LOW mile one. These units aren't built like stuff was in the old days. Anything much over 50k miles (which is a given these days), I'd throughly inspect before installing. Highly recommend changing the seals and bearings too while you're at it. Hopefully you can find one out of a front-end wreck that was well maintained. You'll definitely want to make sure the spider gears have all the tips of their teeth, too ...

Edited December 13, 2020 by Jsdirt